Technical Field
The present invention relates generally to gas turbine engine turbine oil cooling and, more specifically, to outlet guide vanes containing heat exchangers used to cool the oil.
Background Information
Gas turbine engines are commonly provided with a circulating oil system for lubricating and cooling various engine components such as bearings, gearboxes, electrical generators, and the like. In operation, the oil absorbs a substantial amount of heat that must be rejected to the external environment in order to maintain the oil at acceptable temperatures. Electric generator oil cooling typically uses one or more air-to-oil heat exchangers sometimes in series with fuel-to-oil heat exchangers and fuel return-to-tank systems in a complex cooling network.
Compact heat exchangers also known as brick coolers or surface coolers have been used for this cooling but both have a fan air drag penalty. Oil cooling circuits have been suggested that include air-to-oil heat exchangers in vanes in the engine and, in particular, in fan outlet guide vanes (OGVs). The use of OGVs as heat exchangers is a zero fan air pressure loss across the OGVs because oil is routed within the OGVs. Because the OGVs are not finned (less exchange area is available versus a brick cooler or a surface cooler), many OGVs will be needed to cool engine oil or electric generator oil. Routing oil in tiny channels inside an OGV is not free and can be done via oil pressure drop inside OGV channels. A typical air-oil cooler has 50 psid of pressure budget and, as mentioned above, using many OGVs will require much more oil pressure drop than what is currently available or budgeted in an oil lubrication system or an integrated drive generator (IDG) or variable frequency generator (VFG) oil system. Thus, oil cooling systems and circuits using many OGVs as heat exchangers and able to meet air-oil coolers oil pressure drop requirements is greatly needed.